Prestressing reinforced concrete



R E R O H C S H PRESTRESVSING REINFORCED CONCRETE .'5 Sheets-Sheet lFiled Feb. 2l, 1940 if l ...bri .1.

. l, 1942. H. scHoRER PRESTRESSING REINFORCED CONCRETE Filed Feb. 21,1940 3 Sheets-Sheet 2 INVENTOR. HERMA/v Saffo/PER BY W -ATTgNEY Dec. 1',1942. H. scHORER 2,303,394

PREsTREssING REINFORCED CONCRETE F-ild Feb. 21, 1940 :s sheets-sheet sy 1. l, vl. I l

INVENT OR.

BY HERMA/v50# /fE/F' m ATTO EYS Patented Dec. 1, 1942 UNITED STATESPATENT OFFICE.

2,303,394 ransrnasslivc REINFORCED CONCRETEA Herman Scherer, Valhalla,N. Y.

Application February 21, 1940, Serial No.-3Z0,0Z8

(Cl. l2-128) 11 Claims.

'I'he present invention relates to means for prevstressing or applyinginitial compression on reinforced concrete, more particularly to vaprestressing unit by means of which initial compression can be appliedto monolithic reinforced concrete structures of any size andconilguration during the construction process.

Various methods and means have been devised for subjecting concrete toinitial compression for the purpose of reducing or eliminating tensilestresses in the concrete. The prior .art methods and means includedeformation of the moulds and thereby compressing the concrete in themould while the concrete hardens and/or applying initial tension forcesto the reinforcing steel and maintaining such forces until the concretehas-hardened and .then releasing said forces and thereby transmittingAthem to the adjacent concrete and setting up compression therein. Withsome of the prior art methods the bond between the reinforcements andthe concrete is destroyed and monolithic action is not possible. Due tothe fact that the reactions of the tensioning forces are generallytransmitted to the moulds the methods and devices proposed so far areexpensive and their application is limited to the manufacture ofcomparatively small prefabricated concrete elements, such as beams,slabs, piles, pipes, etc. I Y

It is an object of the present'invention to provide a self-containedprestressing device which is independent of the mould and which can beprefabricated in individual units of suitable sizes which can beincorporated in the ileld in the concrete to be reinforced andprestressed .to form a monolithic structure therewith. The units.according to the invention can be used in connection with monolithicconcrete structures of any outside configuration and can be embedded insaid structures wherever precompression is most desirable, i. e.,preferably in such parts of the concrete where later on, when theconcrete is in actual use, tensile stresses occur. tained prestressablereinforcing units according to the present invention can be manufacturedin standardized sizes and conveniently shipped in disassembled orassembled condition. Their application is much more general than that ofconventional methods and devices.

Further and other objects of the present invention will be hereinafterset forth in the accompanying specification and claims and shown in thedrawings which, by way of illustration, show what I now consider to bepreferred embodiments of my invention.

The self-con- In the drawings:

Figure 1 is a side view of the precompressing and prestresslng unitaccording to the present invention.

Figure 2 is a cross sectional view of the unit shown in Figure 1 andtaken along line H- Figure 3 is an end view of the unit shown in'-Figure 1.

Figure 4 is a part sectional view of the unit according to the presentinvention embedded in concrete and in normal operating condition.

Figure 5 is a side view of a modied precompressing unit according to thepresent invention.

Figure 6 is a side view of a modied spacer according to the presentinvention.

Figure 7 is a side view of a -wire contracting member used in the unit.according to Figure 5.

Figure V is a longitudinal sectional view of a modified wire stretchingend member.

Figure 9 is a part cross sectional'and part end view of the memberillustrated in Figure 8 and taken along line IX.-lX of said ligure. I

Figure. 10 is a constructional concrete element reinforced andprecompressed according to the present invention.

Figure l1 is a cross sectional view of the element shown in Figure 10and taken along line XI-XI in said figure.

Figure 12 is a cross'sectional view of the element shown in Figure 10and taken along line XII-XII in said figure.

Like parts are designated by like numerals in all figures of thedrawing. y

Referring more particularly to Figures 1 to I designates alongitudinal-compression member, such as a steelrod of great strengthwhich passes through the center of the spacing members 2 which aredisposed along the rod at regular intervals. Member l which, in case oflarger units,

may consist of a plurality of rods or the like, is

enclosed in athin walled. tube or sheath I0 made of parafiined paper orsimilar material. 'I'he purpose of this tube is to prevent mortar frombonding with the compression rod i, and to permit sliding of the rodwithin tube and spacers. The spacers may consist of cast iron, tile orprecast concrete blocks, having surfaces that willV provide adequatebond when embedded in mortar. Tension means 3 and 4 in the form of thinhigh strength steel wires are disposed around center rod I and placedsubstantially over the periphery of the spacers 2. Two substantiallylike sets of tension means are provided which are wound in steep helicesand in opposite direction around the column formed by the center memberI and the spacers 2. Guide grooves or recesses 2U and projections 2| areprovided on the spacers 2 for keeping the wires 3 and 4 apart andpreventing direct intersection of and kinks in the wires.

'I'he ends of the wires are pairwise interconnected and form loopsaround the lugs 6 projecting from a nut member 5. A bolt 1 is screwedinto the nut member and is provided with a cavity 8 at its threaded endfor receiving the end of compression member I. A steel ball 9 may beinserted in the cavity 8 for reducing friction between rod I and bolt 1and torsion when bolt 1 is tightened. After assembling the prestressingunit bolt 1 in screwed into nut member 5 until tension wires 3 and 4 areuniformly prestressed to the desired extent. The reaction of thecombined tensile forces is transmitted to the compression member I bymeans of the bolt -1 and the steel ball 9.

A tensioning mechanism as described in the paragraph next above' may beprovided at each end or at one end only of the prestressing unit. In thelatter case an end or anchorage member is provided at one end of theunit as shown at the left side of Figure 1. The wires 3 and 4 form loopsaround the lugs 6' projecting from the end block 5. Block 5' is providedwith a cavity 8" holding a ball 9" against which the center rod I abuts.

Warping or buckling of the compression member I, in spite of therelatively high compressive stress in said member, is prevented by thespacers 2 which actv as elastic supports due to the radial force eifectproduced by the tension members 3 and 4. Torsional forces on the endsupports composed of parts 5, 6, and 1 or 5' and 6' are absent onaccount of thetwo series of tension windings arranged in oppositedirections. Theoretical considerations as well as practical experienceprove that, already with a rather steep pitch of the windings of means 3and 4, the necessary stability can be obtained also under extreme stressconditions. unit according to the present invention may be bent to forma flat curve and will snap back into a straight line as soon as theexternal bending forces are removed.

A modification of the prestressed unit according to the presentinvention is shown in Figures 5 to 8. Instead of a single centralcompression member I a compression member is provided composed of aplurality of rods 2| disposed parallel to one another and held togetherby means o f cuil? members 22. To prevent mortar from bonding with thecompression member 2U, said member is surrounded byV means of tubes I0'made of paraflined paper or the like. Instead of two sets of helicalwires 3 and 4, a plurality of Wires 23 are arranged in planes radiatingfrom the central member 20. The wires 23 are spaced from the centralmember by means of spacers 24, illustrated in Figure 6, which have arounded axial outer contour 25 to avoid sharp bends in the wires andwhich have diametrically opposite projections 25 to keep the wiresapartand pairv wise in diametrical planes.

in Figures 5 and 6 can also be used for producing a unit according toFigure 1 instead of the spacers of the type shown in Figures 1 and 2.Undesired contact of the wires of the two sets of wires wound inopposite direction is avoided by placing the wires of one set over thesurfaces 44 on the larger diameter and the wires of the other set overthe surfaces on. the smaller diameter.

Between two spacing members 24 a wheel like contracting member 21 madeaccording to Figure 7 is arranged. Member 21 has openings 29 throughwhich pass the Wires 23 and which openings are disposed on smallerdiameters than the outer and wire supporting surface of the spacers 24.Upon stretching of the Wires 23 thesame are rmly pulled in radialdirection and pressed to the outer surfaces of the spacers 24, by meansof members 21 and the whole structure props up the central member andstiffens the unit against lateral deviations.

For stretching wires 23 and transferring the tension reaction forces ascompressing forces to the central member 20 an end unit may be used asshown on the right hand side of Figure 1. For larger units av mechanismas shown on the right hand side of Figure 5 and in Figures 8 and 9 maybe preferable.. The mechanism consists of a central member 29 of angularcross sectional congurations and having anges 30 and 3I. The tensionwires 23 enter the structure through flared openings 32 in flange 3I andpairwise run along the knurled surfaces 33 and individually into theholes 34 in flange 30. They are firmly and preliminarily held in saidholes by means' of screws 35. After preliminary tensioning and correctsetting of wires 23 and the whole unit, cover plates 36 having knurledsurfaces 31 corresponding to the surfaces 33 are pressed onto the wires23 by means of bolts 39 so that the wires are inescapably held in thestretching end The assembled and tensioned unit. An end plate 39 isplaced in a recess at the left end of member 29 and firmly held theretoby means of bolts 40. The central member 20 passes through a bore 4I inplate 33 into the interior 42 of member 29 and is held in correctposition by means of plate 39. At the other end of member 29 an interiorthread is provided for the threaded bolt 43. This bolt is the equivalentto bolt 1 and its end is also provided with a. cavity 8 containing aball 9' for insertion of and abutting cooperation with one end of thecompression member 20. At the other end of member 23 the same stretchingmechanism as shown in Figure 5 tension members, spacers and tubessurrounding the central compression members become completely imbeddedin mortar.

After the concrete has reached the desired compressive strength, theboards II are removed By releasing the bolts 1 or 43 the compressiveforce in members I or 20 isgradually transferred to the concrete. Theend supports are removed and the tension wires are cut along theexterior face of the concrete. The compression members may also be cutand left in place or may be pulled out for reuse. The tube section nearthe face of the concrete is removed and the small holes are closed witha stiff mortar. Rusting at the end of the tension wires is prevented byrubbing the concrete face with cement mortar or by the vapplication of athin plaster coat I2.4 Under certain conditions it may be advantageousto place the end support nut or the unit 29, 36 inside the form and toleave it embedded in concrete for end anchorage of the tension wires.

After releasing the compression member the initial tension in themembers 3 and 4 is somewhat reduced due to the elastic and plasticdeformation and shrinkage of the concrete, the proportion depending onthe amount of prestress. The balance is available for the -initialcompression of the concrete. The design and proper arrangement of theprestressed reinforcing units permits the complete elimination of al1tensile stresses in the concrete also under extreme load conditions.

Figures 10 to 12 show the application of prestressed reinforcing unitsaccording to the invention to the construction of a concrete girder I1.The units I3, I4 and I5 are placed in a longitudinal direction, so as tocause maximum compression at the bottom of the girder near the center ofthe span I8 and nearly uniform compression over the end faces I9. Forthis purpose units I3 and I5 are placed along the top and bottom side ofthe girder respectively. Units I4 follow the bottom of the girder nearthe center portion and are curved upward toward the ends ofthe girder.The prestressed vertical units IB which are arranged closer together atthe end portion oi' the girder compress the concrete also in verticaldirection. diagonal te'nsion can be effectively eliminated. The usualconsideration of shearing stresses no longer presents a limiting factorin a structure prestressed according to the present invention.

l'If' desired, the holes left by the removed compression members I canbe utilized for drainage, electric conduits, heating or coolingpurposes, etc.

While I believe the above described embodiments of my invention to bepreferred embodi- In this manner the so-called.

ments, I Wish it to be understood that I do not desire to be limited tothe exact details of design and construction shown and described, forobvious modifications will` occur to a person skilled in the art. Y

What is claimed is:

k 1. A'self-contained precompressing mechanism for subjecting concreteto internal compression,

comprising a stretching mechanism, a longitudifor concrete, comprising astretching mechanism including operable means and anchorage' means.

a rodlike central compression member having ends individually abuttingsaid operable means and said anchorage means, sheath means enclosingsaid compression member,A said compression member being slideablymovable in said sheath means, and a plurality of wirelike tensionmembers spaced from and disposed symmetrically around said compressionmember and having. ends individually connected to said anchorage meansand to said operable means.

3. A precompressing reinforcing mechanism for concrete, comprising acentral, column-like compression member, a plurality of spacers disposedon said member and being spaced from one another, a plurality oflongitudinal tension members disposed symmetrically around saidcompression member and resting on said spacers and being thereby spacedfrom said compression member, a stretching mechanism connected to andholding the ends of said tension membersrand abutting said compressionmember and adapted to stretch said tension members and lsimultaneouslytransmit the stretching force reaction thereof to said compressionmember.

4. A self-contained reinforcing mechanism for subjecting concrete topermanent internal compression, comprising a central compression member,a plurality of spacers disposed on said member and being equally spacedfrom one another, two sets of Wirelike tension members helically Woundin opposite direction around said compression member and resting on saidspacers and being spaced thereby from said compression member, anadjustable tension mechanism connected to and holding one end of .saidtension members, and anchorage means connected to the other end of saidtension members, said tensioning mechanism and said anchorage meansindividually abutting the individual ends of said compression member andexerting a pull on said tension members and simultaneously transmittingthe tension force reaction of said tension members to the ends of saidcompression member.

5. A precompressing reinforcing mechanism` for concrete, comprising acentral compression member, sheath means loosely surrounding saidcompression member, a plurality of spacers provided with recesses andprojections disposed on said member and being equally spaced from oneanother by said sheath means, said compression member being freelylongitudinally movable inside said sheath means and said spacers, twosets of wirelike tension members wound hel-ically in opposite directionaround said compression member and spaced therefrom by means of saidspacers, oneset ofksaid tension members resting in said recesses and theother set resting on saidA projections vand being separated thereby fromone another, anda tensioning mechanism including 'a nut member connectedto one of the ends of said tension members and abolt member screwed intosaid nu't member and abutting one end of said compression member andanchorage means connected with the other ends of said tension membersand abutting the other vend or.' said compression member, saidtensioning\ mechanism tensioning said tension members upon relativemotion of said bolt member with respect to'said nut `member andsimultaneously transmitting the tensioning force reaction of saidtension members to said compression member.

6. A self-contained prestressing mechanism for concrete comprising acentral compression member, a plurality of wheellike spacer membersaxially slideably disposed on said compression member, tubular sheathingmeans coaxially and slideably disposed on said compression member andbetween and spacing said spacer members from o e another, two sets oftension wires 'wound in: opposite direction in steep helices around saidcompression member and being spaced from said member by means of saidspacer members, and a tensioning mechanism including a bolt memberhaving a cavity for receiving one end of said compression member, a ballmember disposed in said cavity and affording free rotational movement ofsaid bolt member with respect to said compression member, and includinga nut member connected to one of the ends of said tension wires andscrewed to said bolt member, anchorage means connected to the other endsof said tension wires and having a cavity and a ball member thereinabutting the other end of said compression member, said mechanismaffording tensioning of the tension wires before embedding the latter inconcrete and transmitting the tension reaction' force of said wires tosaid compression member and releasing the tension force in said tensionwiresv after the concrete has sufllciently hardened, thereby subjectingthe adhering concrete to per-V manent internal compression.

7. A self-contained precompressing reinforcing device for concreteconstruction, comprising a plurality of rodlike central compressionmembers disposed in substantially parallel relation to one another, aplurality of spacers and contracting members alternately disposed inspaced relation to one another on said compression member, a pluralityof wirelike tension members laid over said spacers and extending throughsaid contracting members and disposed symmetrically around saidcompression member and held in flat angled zig-zag position by saidspacers and clamped to said central member by means of said clampmembers, and athreaded bolt member screwed into the interior thread ofsaid central member and abutting said compression member, said tensionmembers being stretched and the stretch reaction thereof beingsimultaneously transmitted to said compression member upon rotation ofsaid bolt member relatively to said central member.

8. A self-contained precompressing reinforcing device for concreteconstruction, comprising a rodlike central compression member, aplurality of' spacers and contracting members alternately disposed inspaced relation to one another on said compression member, a pluralityof wirelike tension members laidover said spacers and extending throughsaid contracting members and disposed symmetrically around saidcompression member and held in fiat angled zig-zag position by saidspacers and contracting members, and a tensioning mechanisminterconnecting said tension members and said compression member,

said mechanism comprising a nutlike member connected with said tensionmembers and a threaded bolt member screwed into said nutlike member andabutting said compression member, said tension members being stretchedand the stretch reaction thereof being simultaneously transmitted tosaid compression member upon rotation of said bolt member relatively tosaid nutlike member.

9. A self-contained precompressing reinforcing device for concreteconstruction, comprising a central compression member, a plurality ofspacer members disposed in spaced relation to one another on saidcompression member, a. plurality of wirelike tension members disposedsymmetrically around said compression member and spaced from saidcompression member by said spacer members, and a tensioning mechanisminterconnecting said tension members and said compression member, saidmechanism comprising a hollow central member having an interior threadand an outer surface, a plurality of clamp members having surfacescorresponding to portions of said outer surface and being disposedopposite thereto, said tension members extending individually betweenthe surface of said central member and the surfaces of individuals ofsaid clamp members and being firmly clamped to said central member bymeans of said clamp members, and a threaded bolt member screwed into theinterior thread of said central member and abutting said compressionmember, said tension members being stretched and the stretch reactionthereof being simultaneously transmitted to said compression member uponrotation of said bolt member relatively to said central member.

10. A precompressing mechanism for subjectingA concrete to internalcompression as set forth in claim 1, said compression member beingcomposed of a plurality of individual longitudinal compression elements.

1l. A prestressed reinforced concrete construe tion comprising amonolithic mass of concrete,

a precompressing mechanism disposed at a portion of said concrete masssubjected to tensile or shearing stresses when in normal use, saidmechanism comprising a rodlike compression member removably embedded inthe concrete, a plurality of wirelike tension members substantiallyequally spaced from and disposed substantially symmetrically around saidcompression member and permanently embedded in said concrete mass and inintimate contact therewith, and

a stressing mechanism disposed outside of said concrete mass andabutting one end of said compression member and firmly connected to theends of said tension members, said tension members being tensionedbefore the concrete is placed by means of said stressing mechanism andbeing released and compressing the adhering concrete after the concretehas hardened.

. HERMAN SCHORER.

